Telemetric recording system



3 Sheets-Sheet 1 March 28, 1950 H. D. GIFFEN ErAL 'rELmETRIc RECORDING sYs'ml Filed. Aug. 14.` 1944` 3 sheets-sheet 2 INVENrRs. y 627%@ wl Wam JF' March 28, 1950 H. D. GIFFEN ErAL mmmc RECORDING sys'ma Filed Aug. 14. 1944 @ma Jy March 28, 1950 H. D. GIFFEN er1-AL mmm RECORDING svsm l s sheets-'sheet :s

Filed Aug. 14, 1944 IN VEN TOR. Gfem Patented Mar. 28, 1950 TELEMETBIC RECORDING SYSTEM Harvey D. Gii'en, Theodore, Ala., and Thomas B. Thomson, Jr., San Diego, Calif., assignors to Consolidated Vultee Aircraft Corporation,

San Diego, Calif., a corporation of Delaware Application August 14, 1944, Serial No; 549,440

10 Claims.

It is the general object of the invention to provide a new and improvedA telemetric system.

Another object is to provide a telemetric system comprising a transmitter having a plurality of movable elements or gauges, the changes in position or condition of which are to be transmitted and recorded at a remote point, and means for connecting said elements in rapid and recurring sequence or rotation to modulate the signals sent out by said transmitter over a single channel, a receiver having a corresponding plurality of graphic recording devices at the other end of the channel, means for analyzing the incoming `signals and utilizing them in similar rapid and recurring sequence to operate the graphic recording devices, and means in the transmitter and said receiver for maintaining synchronism between the respective connecting means of the transmitter and the analyzing means of the receiver.

Another object of the present invention is to provide an improved form of transmitting and recording system wherein gauges located at a remote point are scanned in rapid succession and impulses therefrom transmitted over a single channel and recorded, with the changes eil'ected in each gauge recorded on a separate chart, the scanning being done in such rapid and recurring succession that substantially continuous charts may be produced simultaneously with the changes in the gauges.

Another object of the present invention is to provide an improved form of single channel transmitting and recording system having included therein means for producing a synchronizing frequency for transmission (also on the single channel) to a recording means to synchronze the recording on separate charts of the changes of a plurality of detector gauges used at the transmitting station.

Another object is to provide such a transmitting and recording apparatus for use in the testing of aeroplanes in ilight wherein the transmitter is controlled by a large number of independent gauge devices located in various parts of an aeroplane. together with a recording mechanism at a ground station operating in synchronism with the transmitter and having separate chartproducing units, one for each gauge device, so that the changes in the gauge devices are recorded on corresponding charts instantaneously, and in a manner permitting observation at a ground station, of the changes which are occurring in different parts of the aeroplane.

Another object is to provide a flight test apparatus with a new and improved recording apparatus which makes the transmitted data available on the ground simultaneously with the changes occurring in remotely located gauge devices, thereby permitting information as to possible dangers to be transmitted back to the pilot of the plane.

Other objects and advantages will become readily apparent from the following detailed description taken in connection with the accompanying drawings wherein:

Fig. 1 is a circuit diagram of the transmitting portion of a preferred form of the invention.

Fig. 2 is an elementary circuit diagram oi the apparatus at a receiving station.

Fig. 3 is an elementary diagram of a modified form of the apparatus for a receiving station.

Fig. 4 is a more detailed circuit diagram of the sending station of Fig. 1.

Fig. 5 is a more detailed circuit diagram of the receiving station of Fig. 2.

Figs. 6, 7 and 8 illustrate wave forms in diilerent parts of the receiving means.

The invention, in the exemplary form chosen for purposes of disclosure, comprises a means for transmitting variable frequency signalsand for receiving and utilizing these signals to operate a graphic recording means.

The transmitting means, as illustrated in Figs. land 4 and in its essentials, embodies a plurality of gauge devices 60, 6|, 62, a scanning switch A, an interrupting switch B, a driving motor C, an amplifier D, a converting unit E and a transmitter F. The gauge devices are utilized with the transmitting system and feed signals or impulses thereto. When on an aeroplane, for cxample, the gauge devices are located at various stations thereon so as to be individually actuated by changes in condition of the parts or accessories with which they are associated. The gauges used are preferably of the type that can be connected into an alternating current Wheatstone bridge G as two arms thereof and changes occurring at the stations where the gauges are located will produce an oil balance in the Wheatstone bridge to provide a frequency modulated A. C. bridge carrier which is changed in the converter to a varying frequency which, in turn, is fed into the transmitter to modulate the transmitted carrier wave.

Switch B has the same number of contacts as switch A and has its contacts displaced angularly midway between the contacts oi' A. Thus, by having the arms of switches A and B rotate in unison, the arm of switch B makes contact in be- KL, an amplifier M, a synchronous motor 0,.

a power motor P and an apparatus Q which may be of a recording type. Preferably, the apparatus Q embodies a plurality of actuable'elements, one corresponding to and operable in accordance with changes in each gauge device. This apparatus also includes a scanning switch N (Fig. 5) which may be of the same general form as one part of scanning switch A and includes a rotating switch arm and a like number of contacts. The operation of switch N is synchronized with that of switch A so that the signals received at the elements of apparatus Q are in proper correlation with the signals sent out from the various detector gauges.

From rigs. 1 and 2 of the drawings it is apy parent that the complete circuit of a preferred form of the invention lends itself to a partitioning into three main divisions; the first division embodies the apparatus and circuit required in transmitting the signals modulated by various detector gauges located at the station being investigated; the second division concerns itself with the reception of the transmitted signals, the re-conversion thereof to variable D. C. voltages, and the transfer of the signals to the circuit of the recording unit; and the third division embodies the recording unit, various electronic circuits associated therewith, synchronizing means, and the other required apparatus.

The detector gauges may be of any conventional type, depending on the information being soughtv at the station being investigated. These detector gauges preferably comprise a pair oi' resistance elements which are periodically connected in a circuit to form two arms of a Wheatstone bridge. In Figs. 1 and 4 of the drawings, numerals 90, 9| and 92 represent three gauges (of` a group of nine being used) each of which is rshown as embodying two resistance arms 93 and 94y which will comprise two arms of the Wheatstone bridge circuit G, and which are joined at a common point 99. The common points of the various gauges are connected together and a lead 91 connects them to one end of the primary 99 of a coupling transformer 99. A second lead 1| joins the opposite end of the primary 99 to a movable contact 12 of a potentiometer 19, the two ends of which form the other two arms of the Wheatstone bridge. An alternating current generator 14 is associated with the potentiometer 19 and is connected across the ends thereof. The gauges are adapted to be connected in rapid succession across the ends of the potentiometer 13 by the leads 19 and 19, and the leads 11 and 19, and the switch mechanism A. The switch mechanism A, as illustrated, comprises a pair of rotating switch arms 9| and 92, the outer ends of which pass over and engage successively two sets of contacts 93 and 94, one set being arranged annularly about the axis of rotation of each of the switch arms. The leads 11 extending from one end of each gauge 90, 9| and 92 are connected to contact set 93 and the leads 19 extending from the opposite end of the gauges are connected to the second set of contacts 94. By rotating the switch arms Il and 92 in synchronism the gauges are con- 4 nected individually and in predetermined sequence into the bridge circuit.

The motor C, through suitable gearing 19, effects the rotation of the switch arms 9| and l2 at a constant rate of, for example, about ten revolutions per second, so that each gauge 99, 9|, etc., is connected into the bridge circuit in rotation and with predetermined frequency. The invention is not limited to a switch of the type shown or to a mechanical switch, for it is obvious that the switch may assume a variety of forms, either mechanical, electrical or electronic. The number of switch contacts embodied in each of the contact sets 99 and 94 can be varied in accordance with the number of gauges it is desired shall be used. With the switch mechanism A herein shown, nine gauges can be employed: the use of the tenth contact illustrated being explained hereinafter. With a switch mechanism employing eighty contacts a speed of one revolution per second has been found satisfactory.

A coil 95 forms the secondary for the coupling transformer 69 and is adapted to carry the bridge carrier current from the generator 14, as modulated by the successive gauges, to the amplifier D. The amplified signal is then passed through the converter unit E. The circuit representing the converter unit E may be subdivided, as shown in Fig. 4, into the several sections 91, 99, 99 and 9| to segregate the various elements thereof for ease of description. Section 91 includes a conventional rectifier 92, which may be a 6ZY5 rectifier tube, and which rectifies the amplified signals from the Wheatstone bridge G. Associated with the rectifier 92 is a filter 99, of conventional design, and which acts to eliminate ripples that may occur. The direct current signal passed by filter 99 is fed to the portion of the circuit embodying sections 99 and 99. It is here that the various voltages provided by the various gauges are converted into related frequencies. This conversion portion of the circuit comprises two electron tubes 94 and 99; the first tube 94. shown in section 99, is of the 6SK'I type, and

the second tube 95, in section 99, is a gas triode tube of the 884 type. Tube 94 acts as a phase reverser and corrects for non-linearity in the tube 99. A battery 99 provides the power for tube 94,1and a. battery 91 provides the power for tube 95. A resistance associated with tube 94 develops a voltage of the dimension of the voltage of the signal, and this is applied to the grid of tube 99. Tube 99 is an oscillator tube and has associated with it a resistance |09 and a condenser 99 to effect a variable oscillator. Condenser 99 and a resistance |00 will determine the Il ous gauges on the D. C. voltage signals fed into the conversion lportion of the circuit, will act to cause the oscillator, embodying tube 99, resistance |00 and condenser 99, to change its rate of oscillation. The gauges are so constructed that 10 in their condition of maximum unbalance they will cause the oscillator to change its rate of oscillation to a frequency of 4000 cycles. Thus, as a gauge varies, it produces a frequency which varies between 1000 and 4000 cycles in propor- 14 tion to the magnitude of the stress or stimuli acting upon the gauge. These variable audio frequency signals are then fed into section 9| which embodies a conventional amplifier. This amplifier will build up the signals to the proper volume required to operate or frequency modulate the transmitter F. The audio frequency signals will be transmitted by the transmitter to the point where readings are to be recorded.

Before the frequencies are fed to the transmitter they will be interrupted periodically by the interrupting switch B (Figs. 1 and 4) which has an arm |20 connected to ground. Contacts |2| of switch B are connected together and are connected by a lead |22 into the circuit at a .point |23 beyond the converter E. The interrupter switch B and the scanning switch A are both driven by themotor C and in mechanical synchronization but with appropriate gearing 19 provided so that arm |20 of switch B will engage a contact |2| just as the switch arms 8| and 82 leave contacts and will remain engaged until these switch arms reach the next contacts 83 and 84. In this manner there will be effected a periodic shorting out of the audio frequency signals leaving the converter E by periodically connecting the point |23 of the circuit to ground through lead |22 and switch B.

As noted above, the converter E embodiesan oscillator V89 that operates continuously so that the signal at point |23 will be continuous whether the arms 8| and-82 are on contacts 83 and 84 or not, and whether a gauge device is connected in to the bridge circuit or not. A gauge device can only change the pitch or frequency of the oscillations between 1000 and 4000 cycles. Thus every time arm |20 engages a contact |2| there will be a frequency at point |23 that can be shorted out. The signal reaching the transmitter F, as a consequence of the operation of the interrupter switch I I3, will assume the form shown in Fig. A6. As shown, this is a continuous signal having abrupt changes of frequency. It is this signal that is sent by the transmitter F.

At the receiving station (Figs. 2 and 5) the receiver H accepts the incoming signals and passes them into the limiter |04, of conventional construction, and which serves to make all the incoming signals of equal amplitude. The signals are then passed through the phase inverter |05, of conventional design, and into a'conventional power amplifier |06, which will act to provide more undistorted power. The signals are then passed to the discriminator J wherein the variable frequency signals will be reconverted into proportional D. C. voltages. The discriminator J embodies a bridge rectifier |08 (Fig. 5) comprising two electron tubes |09 of the 6H6 type, two tubes being used because they will produce approximately twice the voltage of a half wave rectifier. A pair of discriminator condensers are associated with the electron tubes |09. Two condensers are used to effect a balance in the rectifier circuit though one may be used if the value of that one were changed proportionately. The variable frequency signals received at the discriminator condensers will have a direct relation to the voltage produced across resistance ||2, that is, changes in the reactance of condenser will effect proportional changes of voltage applied across resistance 2. The voltages across resistance ||2 will be directly related to the voltage changes produced by the detector gauges 60, 6|, etc. A fllter |33 of conventional design is provided to eliminate ripples that may occur in the signals.

I'hus the changes in amplitude eilected by the gauges 60, 6|, etc., are converted into proportional' frequencies on passage through the conversion unit E and, after transmission over a single channel, are reconverted, in the discriminator J, into voltages, proportional to the transmitted frequencies. These voltages are then passed to the recording apparatus Q, which is described hereinafter but which is more fully described and claimed in an application Serial No. 549,441, filed by us on August 14, 1944. matured into the Patent 2,485,730, issued October 25, 1949.

In the recording apparatus (Fig. 5) the converted signals are carried by a lead |01 to a rotating arm 21 of the scanning switch N. This switch has a plurality of contacts 28 adapted to be successively engaged by arm 21. As the rotating arm 21 engages each of the contacts 28 a potential will be fed into the electronic analyzing or pen actuating circuits 25 which are connected to the contacts. The circuits 25 are referred to as analyzing circuits because they operate in conjunction with other devices to measure the values of the variable voltage signals and to convert them into proportional time intervals. Generally, one contact 28 and associated circuit 25 are provided for each gauge device or signal source, and the switch N is operated in synchronism with a similar switch controlling-the Y connection of the gauge devices in circuit to produce the D. C. potentials. Each of the electronic circuits includes a condenser 29 and a gas filled electron tube 30 such as a 2051 Thyratron. The 4potential fed to each electronic circuit 25 will charge the condenser 20 therein toa negative f potential equivalent to the strength of the signal being fed. This negative potential will act as a bias on the Thyratron tube 30 to prevent the firing thereof.

The means for effecting the firing of the various Thyratron tubes 30 comprises the potentiometer 22 and a power supplying circuit 35 associated therewith. The potentiometer 22 is shown here as having a' rotatably supported annular resistance element 33 and ten stationary contact members 3| adapted to move successively from a grounded or dead spot 32 (at the advance end of the resistance 33) and across the resistance element 33. A D. C. source 34 applies a voltage to the resistance of the potentiometer. The voltage supplied by source 34 is of a sufficient value to equal the potential of the maximum D. C. signal potential encountered so that the potentiometer 22 will be capable of passing a potential of suflicient magnitude to counteract the effect of the voltage on condenser 29 in a manner and for a. purpose to be described. In the present system the maximum signal voltage is limited to a value of approximately volts. This value is determined by the characteristics of the Thyratron tubes 30 for a potential must be chosen that can be passed without overheating or damaging the tube.

The movement of the movable potentiometer resistance past the contact members 3| of the potentiometer 22 is mechanically synchronized with the movement of the rotating switch arm 21 and each member 3| is associated with a particular electronic circuit 25 leading from contacts 20. The motor P, through suitable gearing and shafting 44', supplies the power for driving the potentiometer resistance across the contact members 3| and for rotating switch arm 21 in step with the signals to be recorded.

To better illustrate the operationof the various parts, one circuit numbered 25a will be traced; this circuit will include the contact 28a in the switch N, contact Sib in potentiometer 22, a condenser 29a, and a Thyratron tube 20a. Thus in circuit 25a with the movement of the switch arm 21 to contact 28a the condenser 20a associated therewith will be charged to a potential equivalent to the potential sent from the impulse source. Movement oi arm 21 oi'l of the contact 22a will disassociate the condenser 29a from the impulse source and at this point the contact lib. acting in the same circuit as condenser 22a, will move from the grounded section 32 oi the potentiometer 22 toward the positive end thereof. The gas illled Thyratron tube Illa will pass current only after the grid potential thereof reaches a voltage determined by the characteristics of the tube and which in this instance, for sake of illustration, will be assumed to be a value of -2 volts.

' In circuit 25a it will also be assumed that there vmit 25a, a potential of 1c vous. when the potentiometer resistance has moved across contact 3ib a suflicient distance to produce a voltage of +8 volts on contact 2lb the effect of the condenser charge will be neutralized and the Thyratron tube 30a will ignite to pass current for a purpose to be described.

During the period that a charge exists on condenser 29a lsumcient to bias the Thyratron a against firing, a potential is being built up on a. second or pen ilring condenser 31a located in the` circuit 25a. A battery 2l supplies the D. C. potential impressed upon condenser 21a and as here used has a capacity of 150 volts. However. the potential required here may be supplied from any D. C. source. A pair oi' resistances Ila and mark at the point through which current is passed. A plurality ot contact strips or trolleys I to Ill inclusive, of equal length, are nxed relative to the metallic rollers l2, and each of the trolleys i to lll is connected into its particular electronic circuit 25. Leads i through l0' effect the connections between ten electronic circuits 25 and the trolleys I to I0. A pen assembly Il is located between the metallic rollers 42 and comprises two drive sprockets Ii and 4l and an endless belt 41, having thereon thirteen equally spaced pens Il, with ten of the pens being active at one time. The motor P which drives the potentiometer 22 and the switch N also drives the pen assembly M through suitable shafting.

It is readily seen that the various pens 4I will not nre simultaneously. but that their moment of nring is dependent on the time that the pen tiring condensers 31 discharge and the discharging of the condensers 31 is dependent upon the firing oi the Thyratron tubes 20 which act in effect as triggers. The time of firing oi the various Thyratron tubes 31| will be, as described, dependent on the potentials impressed on the condensers 29. It is likely that the potentials received from various impulse sources and fed into Thus with ten pens 4l riding on trolleys it is lila are associated with the condenser 21a and battery 3l. Resistance 40a will control the charging rate of the condenser 21a, and resistance 39a acts to pass the charging current of condenser 31a around, or in shunt with, the paper on which charts are laid out. When Thyratron tubea ilres, it will cause condenser 21a to discharge and pass a current into a pen circuit l' to cause a mark to be made through pen lla on a special paper R. used with this invention. Therefore, Thyratron tube 30a, in enect. acts as a trigger or relay. The condenser 21a cannot discharge till Thyratron tube 30a fires and completes the discharge circuit of condenser 21a by grounding the upper side of the condenser through the tube;` the lower side of the condenser being connected through pen circuit t. pen lia and metal roller 42 to ground at 42a. Therefore, the position of the mark made on the paper R with respect to the extremes of each chart will have a direct relation to the potential impressed on condenser 29a from the impulsesource; and this position, therefore, will indicate the dimension of the signal being investigated.

Each of the other electronic circuits 2l will operate in a manner similar to circuit 2in Just described and each will have elements therein similar to pen tiring condenser 31a and resistance "a and 40a and these elements will be numbered respectively 31, 39 and I0. The battery Il is common to all oi the various 'condensers 31, supplying the charge to each.

The printing unit 20. as shown herein in Fig. 5, includes a pair of metallic rollers I2 over which is passed a specialtype of paper R, known commercially as Teledetos paper, and which reacts readily seen that each oi the pens Il can fire at dili'erent times, dependent on the moment that the Thyratron tube Il for each circuit res.

The paper passing over the metallic rollers I2 is divided. as shown, into a plurality oi charts of the width of the trolleys. Each of the pens ll is adapted to act on each of the charts in the course of its movement past each chart. for as one pen Il accepts the charge from a condenser 21 associated with the trolley on which it is riding to eect a mark on the chart adjacent that trolley, a new impulse from the same source will have been fed into the same circuit by switch N by the time the next pen arrives at this trolley and a new charge will be passed to this pen when the associated contact Il of the potentiometer has moved a sumcient distance to produce a p0- tential capable of neutralizing the new impulse to thereby permit the associated Thyratron tube 20 to ilre again and pass another charge from condenser l1. It is here noted that the movement of the potentiometer across contacts 3| is directly related to the movement of the pens Il. for as a pen ll arrives at a particular trolley the corresponding contact 3l (associated with that trolley) will move from the grounded portion of the potentiometer in a direction to produce a counteractlng voltage on the corresponding tube ,30, as described above.

It should be noted that the relationship a pen 4| bears to the trolley on which itis riding at a particular moment will not be the same relationship that the other pens in the system bear to the trolleys on which they are riding. In the ten-chart unit in which the invention has been embodied herein, there will be ten contacts il provided in the potentiometer 22, one for each of the electronic circuits 2t; and a grounded dead spot I2 will occupy one-tenth of the length of the potentiometer. The potentiometer 22 will be assumed to be operated at such a speed that it to a passage of current therethrough to leave a 1| will take one second for it to traverse a contact 9 and to return back to any particular point. There being ten contacts 3| embodied in the potentiometer 22, the contacts will leave the grounded end 32 one-tenth of a second apart. Thus if a particular contact 3|a has just left the dead spot 32, contact 3|b, which follows it, will not leave dead spot 32 until one-tenth of a second later. Because each contact 3| will be traveling nine-tenths of a second on the live portion of the potentiometer- 22 the movement of each pen 4| will be such that it will take a pen nine-tenths of a second to travel from one extremity to the other of a trolley. The pens 4| are spaced apart on the belt 41 a distance greater than the length of a trolley. Thus, if the pen on trolley 3 has arrived at the end of its'trolley, the pen on trolley 4 will therefore be one-tenth of a second from the end of its trolley, and the next pen, which is on trolley 5, will have to travel two-tenths of a second more upon its trolley, etc. Thus there is one-tenth of a second difference, in the amount y of time a pen has ridden on a trolley, between each adjacent pen. This difference in time of travel between each pen is effected to bring the pens into correlation with the disengagement cf the successive contacts 3| of the potentiometer 22, from the dead spot 32 thereon. To insure that each of the pens 4| arrives at the zero point or starting end of a trolley just as -a contact 3| associated with that trolley engages the live por- -tion of the potentiometer` one-tenth of a second spacing between the contacts 3| is carried over to the spacing of the pens 4|. To arrange for the pens to arrive in this manner the trolleys have been spaced apart a distance equal to one-tenth of a seconds movement of the belt. During the interval a pen passes from one trolley to the next, the corresponding contact 3| is moving over the dead spot 32 of the potentiometer.

If the invention were to be embodied in a device having a larger number of charts there will be changes in the time factors involved. For example, in an 80 chart device the potentiometer 22 will have 80 contacts 3| and the contacts 3| will follow each other onto the live portion oneeightieth of a second apart and this dilerence of one-eightieth of a second will be carried to the pens 4| and the trolleys, and each pen 4| will arrive at a trolley one-eightieth of a second later than the pen adjacent to it arrived at its trolley.

It is a feature of this invention that a potential, the duration of which is extremely short, that is, of the order of a few milliseconds, can be noted and an indication made thereof at a deter ined point for investigation. In the form of `he invention herein described it has been shown how the potential received will be stored until the various mechanical elements of the system have had sufficient time to move in their defined paths to analyze and eiect an indication of the impulse. It has also beenv shown that this indication will be directly related to the value of the stored potential.

It is here also noted that though a plurality of detector gauges are being investigated the impulses from these stations will come to the embodiment of the invention over a single channel a'nd in consecutive order, being impressed at conductor |01, from which point the various impulses are fed into various electronic circuits 25v but with all the impulses put out from a particular station being fed into the same electronic circuit.

In the present form of the invention there is provided the additional feature of having the changes of the various gauge detectors plotted on predetermined charts. As switch N rotates to feed the signals received from the various remotely located detector gauges 60, 6| and 62 into the electronic circuits 25, these signals are also fed to a second switch |10 (Fig. 5). However, they are taken oil the line immediately after the receiver H by a lead ||4 because the signal will be stronger here for the purpose desired than if taken oif after they have passed through the discriminator circuit. The switch |10 is driven by the motors O and P, by a gearing connection to the common motor shaft 44', and controls the operation of a plurality of neon tubes |1I, there being as many tubes (ten herein) as there are contacts 83 about the switch arm 8| (Fig. 4). Switch |10, being driven by a synchronous motor O, will be in synchronism with switch A at the detecting station and with switch N at the recording station. As the arm |12 of switch |10 successively engages contacts |13 thereof it will pass the received impulses to light the various neon lamps |1|. At the sending station (Figs. 1 and 4) a rotating switch |40, having a lead to the ground, is provided with a rotating switch arm |40' adapted to engage a contact |4| each time that the switch A completes a cycle of operation. A lead |42 connects contact |4| into the circuit of Fig. 4 at a point |23 where the variable frequency signal leaves the converter unit 86 so that each time contact |4| is engaged there will be a grounding of the circuit and this will effect a dead spot in the signals transmitted to the receiver H. Therefore, when the transmitted signals are fed to switches N and |10 one contact will be dead in each switch for no power isbeing fed to it. The neon lamp associated with the dead contact in switch |10 will therefore not light.

Each of the contacts in the recorder switch N will have a related contact in the indicator switch |10, and each of the contacts of switch N is assocated with a particular trolley on the recorder, so that the changes from only one detector gauge will be noted on each chart. To have the changes of gauge 60 (for example) plotted on the chart opposite trolley and changes in gauge 6| on the chart opposite trolley 2, etc., the dead spot effected by switch |40 in the transmitted signals is arranged to appear when switch arms 8| and 82 of switch A engage contacts 83 and 84 (Fig. 4). These contacts are chosen as the reference point because the contacts of gauge 60 arethe next contacts scanned by arms 8| and 82 and therefore when the dead spot appears at trolley |0 then the signals provided by gauge 60 will appear at the adjacent trolley and will be 'plotted on its chart. Once the dead spot appears at trolley |0 and the signals of gauge 60 appear at trolley the remaining gauges as they are successively scanned will be plotted on successive charts.

As shown, contact |13' of the neon tube lighting switch |10 is related to contact 28 of the recorder feed-in switch N, and contact 28' controls the signal to trolley I0. Therefore, the dead spot received from the transmitter should appear at contact |13', so that its neon lamp does not light, and therefore there will be no signals to plot on the chart opposite trolley I0.

Assuming, as the investigation begins, that the neon lamp associated 'with contact |13' lights up, but that another neon lamp does not, the impulses coming through from the various detector gauges will be plotted on a separate chart for each gauge but not on the desired predetermined chart. To have the impulses from the gauges plotted on the charts as desired, it will be necessary to adjust the system. This can be done by slowing the variable speed motor P until it causes the position of the unlighted lamp to move to the neon lamp I'li' of contact |12', at which point'the motor is brought back up to speed. Thus the dead spot eiected when arms Il and I2 engage contacts I2 and I4 will appear at contact |13' and contact 28', and no charge will pass to trolley I0. The signal of gauge lil will be picked up by switch arms 8l and l2 immediately after leaving contacts 8l' and I4', and this signal will appear at the contacts |12 and contact 28 associated with trolley i because the 'switch arms of switches A, |10 and N are all moving in synchronism and in a clockwise direction.

Rather than by slowing motor P to effect the movement of the position of the unlighted neon lamp, this may be done by rotation of the stator frame ill of the synchronous motor 0. either manually by gearing i2! or by power means (not shown). Rotation of the stator frame I will effect a corresponding phase shift of the rotor and thereby effect a shift of the switch arms of switches I" and N. The dead spot can thus be made to appear at the proper contact.

It should be noted that a means is provided for synchronizing switch N with switch A without the use of interrupter switch B, the synchronous motor O and the rectifier-filter element K. The synchronism can be effected by use of the neonlamp switch |10 and the variable speed motor P by watching the neon-lamps and adjusting the motor speed so that one particular neon-lamp will always remain unlighted. With this condition obtained (and maintained) the various switches are in synchronism. However, the use of the interrupter switch system with a synchronous motor (as disclosed and claimed in our copending application Serial No. 549,442, filed August 14, 1944 matured into Patent Number 2,468,803, issued April 12, 1949) is preferred, for it will automatically keep the invention in synchronism. This system will now be described.

The frequency signal as received by receiver H is of the form shown in Fig. 6 and is sent from the receiver H into two channels (Fig. one channel leading through the discriminator J and the switch N to the apparatus Q. and the other channel leading through the units K, L and M to the synchronous motor O. l

For synchronizing purposes the frequency signal of the form shown in Fig. 6 is i'irst passed through the rectifier K and the signal assumes the form shown in Fig. 7. It is then passed through the tuned filter L and emerges in the form shown in Fig. 8. The frequency of the signal shown in Fig. 8 is dependent upon the number of interruptions effected by the interrupting switch B. If there were 10 contacts embodied in switches A and B and the switch arms are -revolved at such a speed as to touch all of these contacts once each second, and the arm of switch B is/driven at the same speed as the arm of switch A, switch B will make a contact each time that the switch arm of switch A leaves one contact to move to the adjacent contact and thus switch B will act to interrupt the frequency signais being sent out of the converter .10 times each second. The units K and L convert this interrupted signal and effect a new signal of the I. are not concerned with the value of the frequency signals received but take the interrupted signals and utilize the envelopes thereof to produce the alternating current shown in Fig. 8. This A. C., after amplification. is then fed to the synchronous motor 0 w therebyy effect the synchronizatlon of switch N with switch A.

To furnish some of the power for driving the switch N the motor P may be connected intandem with the `synchronous motor O, as illustrated in the drawings. Preferably, the motor P is of a variable speed type, the one herein illustrated being arranged to be operated on a direct current source oi' power indicated by battery I in a circuit embodying a rheostat IBI. In this way the speed of the motor P can be adJusted so that it carries the desired portion of the load of driving the switch N, the synchronous motor O then serving principally as a means for controlling the speed of operation of the switch N and keeping it in step with -the switch A. The invention, it is pointed out, is not to be limited to the employment of a switch N having a rotating arm but may employ a switch of any construction which will operate to perform the desired function.

Although the preferred form of the invention as illustrated in Figs. 1, 2, 4 and 5 is adapted to transmit and record gauge changes substantially instantaneously as they occur, the invention also contemplates that the incoming signals at the receiving station may be recorded for future analysis and use. A disk or a film type recorder T, as shown in dashed lines in Fig. 2, may be connected to receive the .signals from the re- .ceiver H. In Fig. 3 there is illustrateda modiiied circuit including a play-back mechanism U for the record produced by T. This record will contain all of the incoming signals, including the synchronizing signals, so that the output from Vthe play-back can be connected into the circuit of Fig. 3,' which includes all of the elements oi' Fig. 2 with the exception of the receiver. In this way the record may be played again and again when such replaying is desirable for purposes of checking critical changes in any one or more oi' the gauges.

'I'he invention is'particularly useful where it is necessary or desirable to produce charts indicating changes in gauge devices substantially simultaneously with the occurrence of such changes. For example. in connection with the test flight of an aeroplane, as many as eighty or more gauges have been used with an apparatus including a switch mechanism A operating at approximately one revolution per second, so that each gauge would be connected in circuit approximately one one-hundredth of a second at a time. A recording apparatus for such an installation included eight 10 chart mechanisms of the type illustrated in Pig. 5 and so arranged that the pens were displaced approximately oneeightieth of a second apart. With such an apparatus itis possible to have observers at the graphic recorder checking the changes which oc- I of gauge devices embodied in any particular apparatus maybe varied within wide limits.

In our use of the word "telemetering" it is to be understood that oury invention is not to be limited to systems utilizing a transmitter and receiver but that the invention also can be applied to systems wherein ythere is a direct wire connection between the source of intelligence and the recording means as shown by the wire W in dashed lines in Figs. 1 and 2 for connecting the junction |23 to the point 223.

It is thought that the invention and its numerous attendant advantages will be fully understood from the foregoing description; and it is obvious that numerous changes may be made in the form, construction and arrangement of the several parts without departing from the spirit or scope of the invention, or sacrificing its attendant advantages, the form herein disclosedbeing a preferred embodiment for the purpose o! demonstrating the invention; and we do not claim herein either the patentable combinations including specic means for controlling the production of high frequency oscillations in the transmitting system or oi' the transmitting system itself, the same being claimed in a co-pending application Serial No. 535,481, now Patent No. 2.484.218. yissued October 11, 1949; nor the combination including particular features of the recording apparatus and the operation thereof, the same being claimed in a co-pending application Serial No. 549,441; nor the combination forming a telemetric system including a pluralitv of sending stations and the means of operelectrical circuits. to said converter means in synchronism with the rotational sequence of the current -impulses transmitted over said vtelemetric channel, a synchronous motor drivingly connected with said connecting means, and means for producing an alternating current, in step with the transmitted impulses, and feeding said alternating current to said motor, and a plurality oi.' recording devices associated with said electrical circuits, said devices each comprising markingmeans, driving means for moving the marking means withrespect to a record sheet in synchronism with the movement of said connect- V-ing means, and time delay actuating means,

ating the same, as claimed in a co-pending application Serial No. 549,442: nor the combination embodying specific means for accomplishing the frequency variation of signal impulses in repeated succession and the manner of so operating a telemetric system, as claimed in a co-pending application Serial No. 549,443. now Patent No. 2,466,804, issued April 12, 1949; the present invention herein claimed residing in the combinations recited in the appended claims.

We claim as our invention: v 1. In a telemetric system in which current im pulses are transmitted in rotational sequence over a telemetric channel, each 'impulse having a frequency determined in accordance with the. position of an element to be remotely recorded, in combination, converter means for converting said current impulses into proportional D. C. voltages, a plurality of electrical circuits, each including operating means operable after a time delay proportional to the magnitude of D. C. voltage applied thereto, connection means for successively connecting said electrical circuits to said converter means in synchronism with the rotational sequence of the current impulses transmitted over said telemetric channel. and a plurality of recording devices associated with said electrical circuits and operable therebv to indicate D. C. voltage magnitudes, and means to drive said recording devices in synchronism with said connection means whereby the time of operation of said recording devices. by said electrical circuits, after connection of the same is proportional to the magnitude of said D. C. voltages.

2. In a telemetric system in which current impulses are transmitted in rotational sequence over a telemetric channel, each impulse having a frequency determined in accordance with the position of an element to be remotely recorded. in combination, converter means for converting said current impulses into proportional D. C. voltages,l a plurality of electrical circuits, connecting means for successively connecting said operable by said circuits after a time delay following connection of the circuits with the converter proportional to the magnitude of applied D. C. voltage, for actuating said marking means whereby the time of operation of said recording devices, by said electrical circuits, after connection thereof, is proportional to the said D. C. voltages.

3. In a telemetric system in which current impulses are transmitted in rotational sequence over a telemetric channel, each impulse having a frequency determined in accordance with the position oi' an element to be remotely recorded, in combination, y,converter means for converting said current impulses into proportional D. C. voltages, a plurality of electrical circuits, each comprising means for temporarily storing a said D. C. voltage, anelectron tube biased to inactive. condition by such stored D. C. voltage, and power supply means operable in timed relation with said rotational sequence to neutralize said stored D. C. voltage and thus activate said tube, the time of operation of said power supply means in neutralizing said stored D. C. voltage being dependent upon the magnitude of such stored voltage. connecting means for successively connecting said electrical circuits to said converter means in synchronism with the rotational sequence of the current impulses transmitted over said telemetric channel, and a plurality of recording devices associated with said electrical circuits, said devices each comprising marking means, driving means for moving the marking means with respect to a record sheet in synchronism with the movement oi said connecting means, each of said circuits being operatively associated with a corresponding marking means to magnitude of Yoperate the same upon the activation of its associated electron tube, whereby to indicate D. C. voltage magnitudes, the'time of operation of said recording devices, by said electrical circuits, after connection of the same, being dependent upon the magnitude of said D. C. voltages applied to bias said tubes.`

4. In a telemetric system in which current im-v pulses are transmitted in rotational sequence over a telemetric channeL'each impulse having a frequency determined in accordance with the position of'an element to be remotely recorded, in combination, converter means for converting said current impulses into proportional D. C.

-voltages, a plurality oi' electricalcircuits, each amas 11s l cessively connecting said electrical circuits to said converter means, in like rotational sequence, a synchronous motor drivingly connected with said connecting means, and means for producing an alternating current, in step with the transmitted impulses, and feeding' said alternating current to said motor, and a plurality of recording devices associated with said electrical circuits Aand operable by and upon the ionization ofsaid electron tube, and means to move said recording devices in synchronism with said connecting means whereby to indicate D. C. voltage magnitudes, the time of operation of said recording devices, by said electrical circuits, after connection lof the same, being dependent upon the magnitude of said D. C. voltages applied to bias said tubes.

5. In a telemetric system having means for transmitting, in rotational sequence, changes in a plurality oi gauge devices, by means of variable 4frequency signals over a single telemetric channel, in combination, means for converting said signals into proportional D. C. voltages, a plurality of electrical circuits, one for each chart, each circuit embodying a chargeable condenser and an electron tube controlled by said condenser, switch means operated in synchronism with the rotational sequence of said signals to deliver the same in rotation to said circuits for charging the condensers thereof in accordance with the intensity of the converted D. C. voltage delivered thereto, a power supply circuit including a potentiometer resistance, and means for producing a current therein, a plurality of potentiometer contacts, one for each electrical circuit and connected to said chargeable condensers, means for causing relative rotary movement of the potentiometer with respect to said contacts, whereby to change the voltage on the associated condensers until the connected electron tubes operate after intervals determined by the magnitudes of the signal voltages fed to said condensers by said switch means, means for supporting and advancing a plurality of charts, chart marking devices mounted to move continuously in one direction across charts carried on said supporting means, and means for moving said chart marking devices, including a motor operated in synchronism with the rotational sequence of said signals,'said chart marking devices being each operatively connected with a corresponding electron tube circuit and operable thereby to mark the corresponding chart vupon the operation of the associated electron tube.

6. In a telemetric system in which current im- ,g

pulses are transmitted in rotational sequence over a telemetric channel, each impulse .having` a frequency determined in accordance with the y in rotational sequence for the actuation of said trigger means each after an interval, following connection thereof with said converter device, proportional to the value of the D. C. voltage signal applied thereto, and means for driving said recording devices in synchronism with said con- V,verter means whereby said devices may indicate the magnitudes of said D. C. voltage signals.

7. In a telemetric system having means for producing a carrier wave and for frequency modulating said wave successively at unlike modulating frequencies, to provide variable frequency signals, the combination of a receiver for said variable frequency signals. means for converting the variable frequency signals to proportional D. C. voltage signals. a plurality of record sheet marking devices, a plurality of operating means for effecting the operation of said marking devices to indicate D. C. voltage magnitudes, said operating means each including a time delay element, the delayed operation of which is a proportional function of the magnitude of the D. C. voltage signal applied thereto, whereby to determine the time of operation of the connected markingy device, and means for successively connecting said plurality of operating means to said converting means to receive the D. C. voltage signals substantially simultaneously with changes in said variable frequency signals, whereby to operate said plurality of operating means to actuate said record sheet marking devices, the time of operation of said marking devices, by said plu'- rality of operating means, after the connection of said plurality of operating means to receive the D. C. voltage signals thereon, being dependent upon the value of the magnitudes of said D. C. voltage signals applied thereon.

8. In a telemetric system having a plurality of gauge devices, means for transmitting in rapid and repeated rotation signals varying in accordance with the conditions of said gauge. devices and means for producing a synchronizing signal for one gauge device location, the combination of a plurality of recording devices. means operable in like rapid and repeated sequence to direct said synchronizing signal and said varying signals to said recording devices so that each recording device, when acted upon by a varying signal, produces a record of a particular gauge device, an indicating device operable in response to a. varying signal for each recording device and means for utilizing said synchronizing signal and said varying signals in like rapid and repeated rotation for actuating all of said indicating devices but the one to which said synchronizing signal is directed to show the phase relationship of said signal utilizing means with respect to the rotational sequence of the transmitted signals.

49. In a telemetric system having a plurality oi gauge devices, means for transmitting in rapid and repeated rotation signals varying in accordance with the conditions of said gauge devices and means for producing a synchronizing signal for one gauge device location, the combination of a plurality of recording devices, means operable in like rapid and repeated sequence to direct said synchronizing signal and said varying signals to said recording devices so that each recording device, when acted upon by a varying signal, produces a record of a particular gauge device, an indicating device operable in response to a varying signal for each recording device and means for utilizing said synchronizing signal and said varying signals in like rapid and repeated rotation for actuating all of said indicating devices but the one to which said synchronizing signal is directed, and means for adjusting the phase relationship of said signal utilizing means with respect to the rotational sequence of the transmitted signals.

10. In a telemetric system having a plurality of gauge devices, means i'or transmitting in rapid and repeated rotation signals varying in accordance with the conditions of said gauge devices and a synchronizing signal intermediate the signals for two predetermined gauge devices, the combination of a plurality of recording devices, means operable in like rapid and repeated rotation to direct said synchronizing signal and said varying signals to said recording devices so that each recording device, when acted upon by a varying signal, produces a record of a particular gauge device, an indicating device operable in response to a varying signal for each of a number o! said recording devices, means for utilizing said synchronizing signal and said varying signais in like rapid and repeated rotation for actuating all of said indicating devices but the one to which said synchronizing Signal is directed to show the phase relationship of said signal utilizgg ing means with respect to the rotational sequence of the transmitted signals.

HARVEY D. GIFFEN. THOMAS B. THOMSON. Jn.

REFERENCES CITED The following references are of record in the ille of this patent:

UNITED STATES PATENTS Number Name Date 1,361,676 Brewer Dec. 7, 1920 1,388,507 Bell Aug. 23, 1921l 1,641,199 Roucka Sept. 6, 1927 1,849,827 FitzGerald Mar. 15, 1932 1,947,255 Franklin Feb. 13, 1934 2,218,914 Kahn Oct. 22, 1940 2,228,883 Morgan Jan. 14, 1941 2,306,391 Keinath Dec. 29, 1942 2,347,160 Wallace Apr. 18, 1944 2,387,496 Cornelius Oct. 23, 1945 2,378,395 Dickson June 19, 1945 FOREIGN PATENTS Number Country Date 563,934 Germany Nov. 11, 1932 

